Can't multiplayer with my friend

I’m playing Zane and my friend plays Moze, up until recently we’ve had no problem playing together online. He has an iron bear only build and when we try to play cistern of slaughter now, his characters damage and health go severely down in my game. The show me the eridium event also randomly stops working and he says he can tell when Moze is bugged because he will load in already reloading his guns. What could be causing his character to break and the event to break?